This Core will provide critical support to multiple projects of this HIVRAD by providing information on the potency and cross-reactivity of neutralizing antibodies generated by native and novel SIV and HIV-1 envelope glycoproteins. We have assembled a team of outstanding investigators who have combined expertise in all areas of our Core effort. Our goal is to keep pace with the design and production efforts of this HIVRAD by providing timely comparative immunogenicity data. We will conduct irmamnogenicity studies in guinea pigs and rabbits that will include both systemic and mucosal immunity with standard and novel adjuvants. Samples from these animals wilt be assessed for antibodies that neutralize the matched vaccine strain and a wide spectrum of heterologous strains of either SIV or multiple genetic subtypes of HIV-1, as appropriate. In addition, Env-specific binding antibodies will be assessed in serum and vaginal lavages with respect to IgG and IgA classes. The long term goal of this Core C is to determine which immunogens, adjuvants and routes of immunization are capable of inducing neutralizing antibodies that are both potent and broadly-reactive for AIDS vaccine development.